Explosion-proof lighting unit



Aug. 1, 1950 M. J. GRIFFIN 2,517,478

EXPLOSION-PROOF LIGHTING UNIT Filed May 1, 1945 a x i7 0 a Zm eW/d/Patented Aug. 1, 1950 UNITED STATES PATENT OFFICE EXPLOSION -PROOFLIGHTING UNIT Metram J. Griffin, New York, N. Y.

Application May 1, 1945, Serial No. 591,316

4 Claims. 1

The present invention relates to an explosionproof lighting unit adaptedto be used in mines, industrial plants, and other places where anexplosive atmosphere is likely to be present, and where the use ofconventional, exposed lighting units would be dangerous, as constitutinga fire hazard, through the possibility of sparks, arcs or overheating ofparts thereof. Lighting units of this general type are known in the art,and the present'invention may be considered to be an improvement upon,and modification of, the explosion-proof lighting units shown andclaimed in my prior Patent No. 2,304,085.

:As pointed out in the specification of that pat ent, it is important inlights of this type that all parts which might be the source of a sparkor heat, or which might otherwise contribute to the initiation of anexplosion, or a fire, be enclosed within an hermetically sealed space,in which air or some non-combustible, non-explosive gas is maintained atsuper-atmospheric pressure, above a predetermined minimum, to the endthat the explosive atmosphere surrounding the lighting unit may not gainadmission to the inside of the assembly and come in contact with anyexplosion producing elements. By maintaining the pressureabove theambient atmospheric pressure, any tendency toward leakage will beoutwardly and not inwardly of the casing.

Another vital feature is to provide means for automaticallyextinguishing the light, in the event that the pressure within the unitfalls below a predetermined minimum. Thus, if any of the sealsassociated with the lighting unit becomes defective, or if the gas orair under pressure therein otherwise escapes, it is important that thesefacts be indicated, and that the light be extinguished before conditionsbecome dangerous. The bulb circuit must be broken automatically when thepressure in the unit falls below a predetermined minimum, which minimumis still above outside atmospheric pressure.

It isalso important, as pointed out in my prior patent, to make itpossible for a, careless workman to re-inflate the unit and therebyre-light the bulb, on the spot, without removing the unit and having thedefects therein repaired. In accordance with my prior patent, thispractice was preventedby providing a special switch operating mechanismwhich could not be manipulated to re-close the circuit, without removingthe entire lighting unit-from its support. Thus, even though the unitwere re-inflated, the switch would not be operated and the unit wouldhave to be removed in any event.

The primary object of the present invention is to prevent the inflationof the unit while it is supported by the electric outlet fixture, sothat the automatic switch associated with the unit cannot be closedwithout removing the unit from the fixture, and removing it to a placeof safety, Where the defective part may be repaired. Thus, in accordancewith the present invention, it is impossible to inflate the unit in itsnormal operative position and the danger of introducing an inflammableor explosive gas into the casing is entirely eliminated.

A further object of the present invention is to employ, with completesafety, extremely sensitive, positively acting switches so that thepossibility of t e switches failing to open, upon a drop in pressure inthe casing, is completely eliminated.

A further object of the invention is to-provide a novel,simple andfool-proof pressure responsive switch operating mechanism.

Other and further objects and advantages of the'invention of the presentapplication 'will be apparent to those skilled in the art from aconsiderationof the following description of the embodiment shown in theaccompanying drawings, in which:

Figure l is a vertical section, with-certain parts shown in elevation,of the li hting unit.

Figure 2 is a side elevation, on an enlarged scale of the switches andswitch actuatingmechanism, taken from the right of Figure 1.

Figure 3 is a plan view of Figure 2 and Figure 4 is a circuit diagram.

The electric outlet fixturewith which the light ing unit is associated,and by which it is ,supported may comprise a junction box It), carriedby an-electric conduit pipe or other fixed support H, and a terminalsocket housing [2 secured to the junction box by a threaded sleeve I3.The lower'fian'ged end M of the housing l2 carries an internallythreaded locking ring l5, having a threaded lug l6 associated with itsupper flange l7, in'which a set screw it is disposed. The female socketmember 58 is secured in the lower open end of the housing by screws 20,and electric wires 2|, 22 extend upwardlyv therefrom through the centralhollow bore of the housing and the threaded sleeve l3 into the junctionbox NJ, where they are connected to the current lines in conventionalmanner. The joint between the junction box IE! and the housing l2 may besealed, as indicated at 2'3, and the space above the socket member I!)may be filled with a suitable sealing composition, such as-amixtu're oflitharge and glycerol, of substantially the consistency of putty, whichsets hard after a short time.

The lighting unit proper comprises an upper switch housing 25,preferably made in two parts, consisting of an upper half 25a and alower half 25b, secured together by a sectional clamping ring 26,adapted to be drawn tight by screws 2'! threaded in lugs integral withthe ring sections. A packing 28,, disposed in substantiallysemi-circular grooves formed in the upper and lower faces of the endflanges 29, 30 of the housing sections, provides an air-tight joint.

The upper end of the housing section 25a is threaded as at 3|, toreceive the internal threads on the locking ring |5 thereby to supportthe unit as a whole. The open upper end of this member also carries themale plug member 32, held in place by a locking ring 33 and seated upona gasket 34. The prongs 35 of the plug make contact with thecomplemental members of the socket l9.

In the lower housing section 25b there is a bracket 31, held in place bya screw 38 and having upturned end members 39, 46, supporting a pair ofmicro or Mu switches 4|, 42, which are normally open, but which may besnapped to closed position by the application of relatively lightmechanical pressure to the buttons .43 associated therewith, as is wellunderstood in the art. 'A Sylphon type bellows 44, supported on thebracket 31 carries a cross arm 45, projecting over a pair of leafsprings 46, 4! mounted on the switch casings and overlying the switchactuating buttons 43. The bellows is so adjusted that, when atmosphericair conditions exist in the housing 25, the cross arm 45 is spaced abovethe leaf springs 46, and the latter are out of contact with the buttons43 so that the microswitches are open. As explained below, when the airor gas pressure in the housing 25 is raised above a predeterminedminimum, the bellows and the air'within its interior are contracted andcompressed, thereby moving the spring fingers 46 into forceful contactwith the buttons 43 to close the switches and to maintain them closed,as long as the air or gas pressure is maintained above a predeterminedminimum. i

At its lower end, the housing section 251) ter-' minates in a threadedneck 56. receiving a looking ring 5|, adapted to clamp the upper,inturned flange 52 of alight casing 53 in position, between gaskets 54,55, making an air-tight joint. The neck 56 also carries an internallythreaded collar 56, which supports a plate 57 of insulating materialcarrying a bulb socket 58 and terminal connections 59, 60.

The light casing or reflector 53, made'of spun aluminum or any othersuitable material, terminates at its lower end in an angular flange,including an outwardly directed portion BI and a downturned portion 62.The latter is adapted to bite into a U-shaped gasket 63, of rubber,Neoprene or the like, embracing the outer edge of the lens 64 and heldin place by an L-shaped metal band 65. A sectional clamping ring 66 hasoneflange 6'! underlying the ring 63 and another flange 68 disposed uponan inclined surface engaging the flange 6| of the light casing. As theclamping ring is contracted, by tightening screws 69'threaded in lugs16, the downturned flange 62 of'the light casing is forcefully-embeddedin the gasket 63, thereby providing an hermetic seal. The clamping ringmay be made in three, four or more sections.

i The electric light bulb carried by the socket 4 58 is supplied withcurrent by wires 16, 11, one leading to one terminal of one of themicroswitches and the other leading to one terminal of the other switch.Wires I8, 19 lead from the other terminals of said switches,respectively, to the two prongs associated with the plug 32, connectedin turn through the socket l9 to the current lines. Hence, if eitherswitch opens, the bulb circuit is broken.

The flange 29 of the upper switch housing section a. is apertured at 80and counterbored and threaded at 8| for the reception of a valve nipple82, which may be of conventional design and which may contain a standardautomobile tire valveassembly. It will be noted that the upper open endof the valve nipple is disposed directly below, and is obstructed by,the flange 83 of the locking ring l5. Hence, when the parts are inassembled position, as shown in Figure 1, access to the inflating nippleis blocked by the locking ring, and it is impossible to place an airhose or inflating chuck thereon to introduce air or gas into theinterior of the lighting unit. It will be understood that the interiorof the switch housing and of the light casing 53 are in freecommunicaiton with each other, but that the space within these membersis sealed from the outside, by the gaskets 34, 2B, 54, 55 and 63.

In the operation of the lighting unit in accordance with the presentinvention, after the elements of the unit have been assembled, andbefore it is attached to the outlet fixture, air or a non-inflammablegas, such as carbon dioxide, under'pressure is introduced through thevalve nipple 82. This will cause the bellows 44 to contract, therebymoving the leaf springs 46 into contact with the switch actuatingbuttons 43 and closing both switches. Hence, the circuit from the prongs35 through the switches to the bulb 15 will be completed. The unit isinstalled by first cutting ofI' the line current to the socket til, theninserting the prongs 35 into the socket and screwing the locking ring I5 upon the threads 3| of the housing section 25a. Set screw |8 istightened, and the installation is complete. When the line current isturned on, the bulb will be illuminated. In the event of a leak of gasfrom the interior of the switch housing or light casing, so that thepressurefalls dangerously, the bellows 44 will expand, thereby liftingthe cross bar 45 and the leaf springs 46, permitting the switches 4| and42 to open and extinguish the light. Although it is not essential toemploy two switchestheir use is preferred, so that, in the event thatone should fail to operate, the other will be certain to function andopen the circuit. Moreover, the use of a switch in each line to the bulbis an important safety factor in that it prevents the possibility of asingle switch, in one line only, from being by-passed or shunted out ofthe circuit by contact between that line and the conduit or lightfixture above the switch and similar contact between that line and thelighting fixture below the switch. I Such accidental contact betweena'line and the metal parts of the conduit or fixture would establish aflow of current around the switch so that, even if the air pressurewithin the casing fell to atmospheric pressure, and the switch wereopened, the circuit would still be maintained and the light would not beextinguished. However, if two switches are used, one in each line, thiscontingency cannot occur, since one switch will, inevitably, be openedwhen the pressure falls, thereby extinguishing the light.

It will be impossible for a careless workman to attempt to re-illuminatethe light by pumping air or inflammable gas into the interior of theunit, because the valve nipple 82 is blocked by the locking ring [5.Hence, the lighting unit must be removed. It has been found in practicethat, if a workman goes to the trouble of removing a defective lightingunit, he will replace it with a properly functioning one, rather thanre-inflate and replace the defective one.

The present invention is not limited to the details of constructionshown in the accompanying drawings and described above, as manymodifications will occur to those skilled in the art, from aconsideration of this description. All such modifications as come withinthe scope of the appended claims and their equivalent are intended to beincluded.

I claim:

1. In combination, an explosion-proof lighting unit and an-electricoutlet fixture having electrical terminal connections and an internallythreaded, laterally flanged locking ring associated therewith, said unitcomprising casing means defining an hermetically sealed space removablysupported by the locking ring, a bulb in said space, electric circuitmeans leading from the terminal connections to the bulb, switch means insaid circuit adapted to be closed by the application of predeterminedmechanical pressure and to be opened by the release of said pressure, abellows in the space movable in response to changes in the gas pressurein the space, an arm carried by the bellows connecting the bellows tothe switch, whereby the switch is maintained closed or open, accordingto the pressure in the space, and a valve nipple projecting upwardlyfrom said casing means for admitting air or gas into the space to raisethe pressure therein and thereby to close the switch, the upper end ofthe nipple being disposed directly below and being obstructed by theflanged locking ring when the latter supports the casing means, wherebythe nipple is accessible for introduction of air or gas into the spaceonly when the unit is removed from the outlet fixture.

2. An explosion-proof lighting unit and an electric outlet andunit-supporting flxture having electrical terminal connections and aninternally threaded laterally flanged locking ring associated therewith,said unit comprising a casing removably supported by the locking ringand defining an hermetically sealed space, a bulb in said space,electric circuit means leading from the terminal connections to thebulb, switch means in said circuit adapted to be closed by theapplication of predetermined mechanical pressure and to be opened by therelease of said pressure, a bellows in the space movable in response tochanges in the gas pressure in the space, an arm for transmittingmechanical pressure from the bellows to the switch, whereby the switchis maintained closed or open, according to the pressure in the space,and a valve con- (luit projecting upwardly from said casing foradmitting air or gas into the space to raise the pressure therein andthereby to close the switch, the open end of said conduit being blockedand rendered inaccessible by the flange of the locking ring when theunit is supported by said fixture, whereby the unit must be removed fromthe fixture before additional gas or air may be introduced thereinto.

3. An explosion-proof lighting unit and an electric outlet andunit-supporting fixture having electrical terminal connections and alaterally flanged, internally threaded locking ring, said unitcomprising casing means defining an hermetically sealed space, a lightbulb therein, a normally open microswitch in said space in circuit withthe bulb adapted to be maintained closed by relatively light mechanicalpressure and to be opened automatically by relief of said pressure, abellows responsive to changes in the gas or air pressure in the space,an actuating arm carried by the bellows for applying and relieving saidpressure from the bellows to the switch, whereby the switch is closedwhen the pressure in the space is above a predetermined minimum and isopened automatically when the pressure falls therebelow, and a valveconduit projecting upwardly from said casing means for admitting thereinair or gas to said space to raise the pressure in said space, saidconduit being blocked by the flange of said locking ring and beinginaccessible when the unit is supported by said fixture, whereby theunit must be removed for purposes of inflation.

4. An explosion-proof lighting unit adapted to be supported by anelectric outlet fixture having electrical terminal connections and unitsupporting means associated therewith, said unit comprising meansdefining an hermetically sealed space, a light bulb therein, an electriccircuit including two lines leading to said bulb, a pair of normallyopen micro switches in said space adapted to be closed by relativelylight mechanical pressure, each switch being connected in one of the twolines leading to the bulb, a bellows in said space movable in responseto changes in the gas or air pressure therein, means for admitting airor gas under pressure into said space and thereby to positively movesaid bellows, a rigid mechanical connection between the bellows and eachswitch to transfer mechanical pressure to the switches to close thesame, said bellows being positively movable in the opposite directionupon a predetermined drop in the pressure in said space to relieve saidmechanical pressure through said connection and to eflect opening of atleast one of said switches.

METRAM J GRIFFIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 562,208 Waegel June 16, 1896583,959 Waegel June 8, 1897 1,294,806 Hunt et a1 Feb. 18, 1919 2,304,085Griffin Dec. 8, 1942 FOREIGN PATENTS Number Country Date 29,344 GreatBritain 1911 525,657 Great Britain Sept. 2, 1940 853,977 France Dec. 23,1939

